This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. ABSTRACT: The mammalian kinetochore is a multi-component, proteineous complex whose dysfunction is linked to a number of major health problems including cancer, birth defects, and miscarriages. The kinetochore's essential role in genomic segregation makes it an attractive target for developing chemo-therapeutic agents that inhibit cell division in diseases such as cancer and immuno-proliferative disorders. The kinetochore functions during mitosis include: 1) attaching chromosomes to the mitotic spindle; 2) controlling the dynamics of kinetochore microtubules; 3) generating force for chromosome alignment;and 4) generating a cell cycle checkpoint that delays anaphase onset until all chromosomes are attached to the mitotic spindle and aligned at the spindle equator. Intricate interactions between kinetochores and microtubules (MTs) are essential for all of these vital processes. Despite rapid progress in identifying molecular components of the kinetochore, understanding of the underlying mechanisms of kinetochore function and its interactions with microtubules is just beginning to unfold. This is due in part to the paucity of structural information concerning how different kinetochore molecular components are arrange relative to each other and to attached kinetochore microtubules. The McEwen lab is using electron tomography and serial-section electron microscopy to determine how specific molecular components enable the kinetochore to maintain dynamic attachments to spindle microtubules. Previously, we used electron tomography of high-pressure frozen and freeze-substituted specimens to determine the structure of the kinetochore outer plate and demonstrate that microtubule dynamics is not coordinated or tightly controlled by the kinetochore. These same studies also established that the kinetochore outer plate is the termination point for about 90% of kinetochore microtubules, that the outer plate exhibits a substantial structural rearrangement upon microtubule attachment, and that outer plate forms two distinct attachments to kinetochore microtubules: lateral attachment to the microtubule walls and radial attachments to the microtubules tips. The study was featured as a highlighted paper in the last RVBC progress report. + Dong, Y., K.J. VandenBeldt, X. Meng, A. Khodjakov, and B.F. McEwen (2007) The outer plate in vertebrate kinetochores is a flexible network with multiple microtubule interactions. Nature Cell Biology 9: 516-522. [With cover picture;"Faculty of 1000" recommended].